Transfer presses are used for making automobile body parts, for example, or other large-surface sheet metal parts used in the automobile industry. The sheet-metal parts to be produced have widths and lengths of up to several meters and are formed from flat metal sheets in a multi-stage metal-forming process. The sheet-metal part dimensions thus determine the tool dimensions for the various metal-forming stages and the transfer presses are correspondingly large.
U.S. Pat. No. 5,140,839 discloses a transfer press with a press frame, comprising press supports, press tables or press plates and headpieces or crown pieces. Rams that can be moved up and down with a press drive are installed above the press tables. Sliding tables for accommodating tools are assigned to the press tables, with the lower tool being fixedly connected to the sliding table and the upper tool being connected to the press ram. Each sliding table and each press ram carries respectively several tools. A transfer device with suction bridges is provided for transporting the work pieces between the tools, meaning from press stage to press stage. Each suction bridge takes the form of a cross or transverse member provided with suction spiders that function as holding devices. The suction bridges are moved with the aid of lifting and transporting units that are arranged in a narrow intermediate space between the tools and the press support on both sides of the tools, which extend respectively in a longitudinal direction through the press. Pairs of the lifting and transporting units respectively carry one suction bridge with their ends. The length of one suction bridge is longer than the width of a tool, so that the ends of the suction bride project on both sides from the tool if the suction bridge is located inside the tool.
A transfer press, which operates with a suction-transfer system, is also known from reference European Published patent application EP 0388610 A1. In contrast to the above-described transfer press, the transfer press according to EP 0388610 A1 is provided with just one tool below each ram. Running rails for guiding the suction bridges extend on both sides of the tool through the transfer press. The suction bridges project on both ends past the tools and are held on carriages running along rails. Between the press supports and the tools, a considerable amount of space must be provided for the rails, the carriages and the associated units. Conversely, the space spanned by the press supports can be utilized only partially for the existing tools.
A different problem appears when using older tools that were originally provided for the operation of single presses. Tools of this type sometimes are provided with guides that operate between the upper tool and the lower tool and are arranged on the side of the tools. Guides of this type stand in the way of mechanization through a traditional suction transfer.
German published patent application DE 195 21 976 A1 deals extensively with the work piece transport in presses for large parts, wherein press lines with individual presses, arranged at relatively large distances from each other, as well as press lines with presses arranged adjacent to each other are considered. FIG. 38 of the document discloses a hinged-arm feeder for transporting parts from press to press, provided these are set up at relatively short distances to each other. The feeder is provided with a vertically adjustable carrier, e.g., held by means of a guiding device on a cross bridge that connects two press supports. The slide carries a pivot drive that acts upon a crank. The pivoting end of the crank is connected to a suspended lever parallelogram, the upper end of which is guided on a slide so as to be freely displaceable in the vertical direction. The lower end of the lever parallelogram, on the other end, carries two guide rods that are hinged to each other, with one of the guide rods being connected to the parallelogram and the other of the guide rods being connected to a suction spider. A planetary gear is arranged at the lower end of the parallelogram, which translates the pivoting movement of the parallelogram into a pivoting movement of the respective guide rod supported by it. The planetary gear thus causes a forced-motion coupling. The joint connection between the two guide rods, supported by the parallelogram, is positioned by means of a toothed belt that moves the two guide rods of necessity against each other when the parallelogram is pivoted.
For the linear transport movement, the parallelogram pivots from one pivoting end position, in which both guide rods project outward from its lower end, initially into a lower position in which the first guide rod points upward in a perpendicular direction and the second guide rod is suspended from there perpendicular in a downward direction and then moves past this position and into its other extreme position where both guide rods extend in the other direction.
The total energy required for accelerating and decelerating the drive and the sheet metal parts is provided by the crank drive.
In addition, the bridge provided for supporting and positioning the transfer device requires a certain structural space between the supports, which is particularly narrow if the individual press stages of neighboring presses are arranged very close together. In particular, this is true for hybrid press systems where adjacent presses respectively share a common support, with the spacing between the tools of neighboring presses being so narrow that no intermediate repositories are provided between the supports.
Starting with this, it is the object of the present invention to develop a transfer press that permits an improved use of the space between the press stages that is spanned. It is furthermore the object of the invention to design the transfer device such that short transfer times and an exact tool positioning can be achieved.